go to the "source" view of the XPage and search for 

refreshMode

and look for "complete" versus "partial"

I do have some "complete" refresh modes, but not with any of the event based activities that are causing this problem.  Thanks for the tip, though.

I'm not sure what the issue is.  Up until the most recent version of Domino I didn't think you could add a file attachment via Partial Refresh.  It had to be complete.

I'll just through out this - I'm working on an attachment storage project - fileVault  (http://notesin9.com/index.php/2014/08/01/notesin9-150-announcing-filevault-for-xpages/)  

The code and videos on how to set it up will be coming to the NotesIn9 Screencast very soon.

Might be interesting to you...

As I mentioned, the page has one upload control.  If I select a file, fill in a description and save the document, then it all works fine.  If I select a file, fill in a description and then click a radio button that performs a partial refresh - then I'll get another file attachment, click the radio button again - I get another attachment.  AND the radio buttons are set to only refresh ONE ELEMENT on the page (a computed value).  The partial refresh does not include a panel with the upload control in it.

This is driving my customer crazy, because users will regularly click items on the page - and each click seems to save their file again as another attachment!